Monkeys will be raised for the first 3 years of life with living mother substitutes or with inanimate surrogates. Effects of rearing conditions on sympathetic and para-sympathetic interactions, on endocrine profiles, and on behavior will be determined by measuring activity under normal (non-stressed) conditions, and in response to a variety of experimental procedures. The onset, development, generality, and persistence of inter-group differences in behavior and physiological profiles will be established by collecting longitudinal data over a broad range of situations.